1. Field of the invention
The present invention relates to a presensitized light-sensitive lithographic plate, and more particularly to a simply processable presensitized lithographic plate (hereinafter referred to as PS plate).
2. Description of prior art
PS plates which have a light-sensitive layer formed by coating the surface of an aluminum support with a composition comprising silver halide and a vinyl compound are described in Japanese Patent Provisional Publications Nos. 57(1982)-211146 and 58(1983)-16231. Processes for preparing a lithographic plate from the PS plate comprise: a step (exposure step) of subjecting the PS plate to pattern exposure; a step (development step) of immersing it in a developing solution, washing it with water and dissolving out the light-sensitive layer in the unexposed parts; and a step of coating the surface of the aluminum support with gum arabic and the like to prevent decrease of hydrophilicity which is likely caused when the surface (where the light-sensitive layer has been removed) of the aluminum support is exposed to air. The PS plate utilizing light sensitivity of silver halide is advantageous because it is highly sensitive. However, as described above, the above-mentioned methods need a wet development process employing a developing solution to remove the light-sensitive layer. Therefore, these methods require complicated steps and sometimes may cause problems with respect to hygiene and environmental pollution according to reagents to be used.
Another process for the preparation of a lithographic plate utilizing wet development is disclosed in Japanese Patent Provisional Publication No. 58(1983)-224752. The disclosed process utilizes a presensitized lithographic plate having a light-sensitive layer containing a polymerizable compound which is enclosed with microcapsules having a hydrophilic wall and comprises the steps of: imagewise exposing the light-sensitive layer of the presensitized lithographic plate to a radiation; breaking the microcapsules within the unexposed area of the light-sensitive layer; and thereafter exposing the whole surface of the light-sensitive layer to a light to cure an unpolymerized polymerizable compound. In thus obtained lithographic plate, the exposed area serves as a non-image portion and the unexposed area serves as an image portion. Therefore, this process requires use of hydrophilic microcapsules for enclosing the polymerizable compound therein. Since the use of hydrophilic microcapsules sometimes is not advantageous in practice, a process for the preparation of a lithographic plate involving a transfer step which is free from the limitation to the use of hydrophilic microcapsules is proposed in Japanese Patent Provisional Publication No. 61(1986)-281242.
Various PS plates which have a light-sensitive layer containing a photo polymerizable compound or the like instead of the silver halide, and a hydrophilic layer (e.g., undercoat layer, intermediate layer) is provided between a hydrophilic support and a light-sensitive layer are described in Japanese Patent Provisional Publications Nos. 49(1974)-102403, 51(1976)-71123, 56(1981)-127493 and 57(1982)-125095, and Japanese Patent Publication No. 51(1976)-15764. The PS plate comprising a hydrophilic layer, although it depends on characteristics of the substance which constitutes a hydrophilic layer, has an advantage in that occurence of scumming can be reduced compared with the PS plate comprising a light-sensitive layer directly arranged on a support.
A PS plate comprising a light-sensitive layer containing silver halide, a reducing agent, a polymerizable compound and a hydrophilic binder on a hydrophilic support wherein the silver halide, the reducing agent and the polymerizable compound are contained in lipophilic microcapsules which are dispersed in the light-sensitive layer has been already disclosed in a copending U.S. Ser. No. 116,352.